Repair of damage to DNA caused by radiation treatments appears to involve several different mechanisms, among which are some of the pathways also involved in genetic recombination. The control and function of recombination and repair processes can be advantageously studied in organisms with relatively rapid growth rates, such as bacteria, which must of necessity repair any damaged DNA quite rapidly. Recent work by Birge and Low has demonstrated that, in Escherichia coli, two of the three best studied recombination deficiency mutations which are known to cause increased sensitivity to ionizing radiation are also associated with the appearance of partially recombinant DNA molecules. The proposed project is an attempt to remove these recombinational intermediate structures from the cell and to characterize their structure by electron microscopy and various physical chemical techniques. In addition, a further search for new recombination deficiency mutations which might produce other types of intermediate forms of recombinant DNA is proposed. It is hoped that these studies may eventually lead to a sequencing of the steps involved in the production of recombinant DNA and elucidate one potential mechanism for DNA repair.